Build the Chili Butter: Heat your skillet to medium-high. Add butter, garlic, and chili flakes to the same pan. Cook 15–20 seconds, stirring constantly, until fragrant.
Cook the Pasta in the Pan: Stir in soy sauce, fish sauce, sugar, salt, and water (about 4½ cups). Raise your heat to high. Add spaghetti to the skillet. Bring to a simmer.
Reduce & Gloss: Cook, stirring frequently and turning noodles as they soften. As the water reduces, it forms a glossy, spicy sauce that coats the pasta. Once the water reduces half way, add in your shrimp.
Finish: Add lime slices and toss until shrimp are warmed through and the sauce looks loose and shiny. Finish with sliced scallions and additional chili sauce.
